The discovery was made while investigating improvements to the newly developed plastisol carbon paper, the subject of U.S. patent application Ser. No. 591,856, filed June 30, 1975, now U.S. Pat. No. 4,028,286 granted June 7, 1977, for an "Ink Transfer Member," by Joseph D. Neri and John L. Williams, and assigned to the assignee of this application, incorporated in its entirety herein. Plastisol carbon paper had been earlier developed by Kee-Lox Manufacturing Co. (Harvey, U.S. Pat. No. 2,893,890) and Burroughs Corporation, Ralph H. Clark, U.S. Pat. No. 2,989,493, issued June 20, 1961.
While the earlier plastisol suggestions were interesting, the main part of present day production of carbon paper are either hot wax or solvent carbon paper, as developed by the same Ralph H. Clark, see U.S. Pat. No. 2,944,037, issued July 5, 1960. Solvent carbons have a tendency to add pollutants to the atmosphere during manufacture and considerable difficulty has been encountered with hot wax carbon in view of the softness of the wax layer and its tendency to mark anything it comes in contact with. The improvement in the above-referenced application suggested the use of a liquid polyglycol of low vapor pressure at the fusion temperature of the polyvinyl chloride plastisol. The polyglycol has the properties of low viscosity at ambient temperature, substantial insolubility in water and an effective dispersant for colorant materials. It serves as a vehicle for the liquid ink suspended within the pores of a matrix type polyvinyl chloride plastisol. The desirable result of reduced smoke was accomplished with addition of only enough substantially non-water soluble and non-hygroscopic polyglycols to meet the air pollution and write intensity requirements. This was suggested because polyglycols are more expensive than the other oils utilized as non plasticizing oils, even though it was suggested that in the polyvinyl chloride plastisol composition the polyglycol can replace all of the oil vehicle. The plasticizers utilized were unaffected. These were typically esters such as dioctyl phthalate, dibutyl phthalate, tricresyl phosphate, triethylene glycol di-2 ethyl butyrate and others which are well known widely employed polyvinyl chloride plastisols formulations.
It was known by earlier experiments that water in small amounts was not detrimental to the fusion of the polyvinyl resin.
Even organosols, i.e. plastisols thinned with a volatile solvent were found to be substantially unaffected by the addition of small parts of water to the solvent before fusion.
Hydrosols were well known, as was the commercial practice of plasticized water soluble resins. Polyvinyl alcohol is a well known water soluble resin often plasticized with glycerine when used in vacuum bag molding. A cold water soluble type polyvinyl alcohol is also used in packaging and barrier films.
However, plasticized polyvinyl chloride and polyvinylidene chloride copolymer films have become so well known for their properties, chemical resistance, low water absorption, good tensile and tear strength that when the term plastisol is used, reference is made, as it is here, to the use of finely divided thermoplastic water insoluble vinyl based polymers, dispersed in a solution to form a relatively viscous dispersion. An organosol is a plastisol in which the solution contains an organic volatile thinner or solvent for the plasticizer such that the organosol is consequently less viscous than the plastisol but is similarly used. As the plasticizers of these water insoluble vinyl polymers were oil based, typically esters, the solvents used, as thinners were also oil based. The typical dispersants include for instance methyl ethyl ketone and acetone, which hydrocarbons of low viscosity and low solvating types are used to balance the dispersants.